arc: add explicit selection of CPU templates ARC 750D and ARC770D

This separation allows to specify unique options and features for each
CPU.

For example ARC 770D has LLOCK/SCOND instructions built-in by default.
Also this new scheme simplifies selection of proper configuration for
users - preconfigured options now match templates for ARC CPUs.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Anton Kolesov <akolesov@synopsys.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

arch/Config.in.arc

@@ -1,6 +1,22 @@
-# Choise of atomic instructions presence
+choice
+	prompt "Target CPU"
+	depends on BR2_arc
+	default BR2_arc770d
+	help
+	    Specific CPU to use
+
+config BR2_arc750d
+	bool "ARC 750D"
+
+config BR2_arc770d
+	bool "ARC 770D"
+
+endchoice
+
+# Choice of atomic instructions presence
 config BR2_ARC_ATOMIC_EXT
 	bool "Atomic extension (LLOCK/SCOND instructions)"
+	default y if BR2_arc770d
 
 config BR2_ARCH_HAS_ATOMICS
 	default y if BR2_ARC_ATOMIC_EXT
@@ -18,4 +34,5 @@ config BR2_ENDIAN
 	default "BIG"	 if BR2_arceb
 
 config BR2_GCC_TARGET_CPU
-	default "arc700"
+	default "arc700" if BR2_arc750d
+	default "arc700" if BR2_arc770d